Lithograph plate



Patented Apr. 11, 1939 UNITED STATES PATENT OFFICE No Drawing.

Application June 28, 1935.

Serial No. 28,872

. 3 Claims. (01.101-4014 My invention relates to a plate adapted to beused in lithography, either oifset or direct.

Heretofore such plates have 'been made of stone or of metal such as zincor aluminum.

The object of my invention is to make a plate of paperwhich shall havethe properties necessary for successful commercial use in place of themore expensive'stone or metal plates. Such a paper plate must be strongand pliable and pref erably of a light color so that the ink impressionsthereon will'be conspicuous. Its surface should be such as to standdrawing, printing, typing or painting. The surface may desirably besensitized so as to receive photographic impressions. The surface shouldbe such that all marks can be readily erased or otherwise corrected.

In the practice of my invention I first take a sheet of waterproofpaper, that is, the paper must be sufllclently waterproofed so thatitwill not expand when wet even to the very small extent-which would bedeleterious in its use as a plate for lithography. Sheets of suchwaterproof paper may be prepared in many ways. A' preferred sheetcomprises two layers of waterrepellent paper stuck together by anintermediate layer of asphaltum. Such a composite sheet I have foundvery satisfactory for my purpose. A single sheet of paper, that issufficiently waterproof by reason of chemical treatment or otherwise,will, however, answer the purpose.

I then apply to one or both surfaces of this paper sheet, which iswaterproof as above described, a coating of a material such that thesurface of the coated paper will have a substantially equal aflinityboth for the water (which may or may not be chemically treated) used inlithography and for the grease comprised in the marking materialscommonly used in preparing lithographic plates and in the ink used inlithography. I refer herein to such water as lithography water and tosuch grease as lithography grease.

While various mixtures or compositions of materials may be used forcoating the surface of the paper plate and imparting to it the desiredaflinity for lithography water and grease, I have found that one verysatisfactory coating, which I give by way of example, consists of amixture of silica or clay (aluminum silicate) or other suitable filler,a binder such as casein, starch or glue, and a waterproofing compoundsuch as formaldehyde or aluminum acetate. I have found a coatingconsisting, for example, of 40 parts by weight of 10% alkaline caseinsolution or a true solvent solution of casein, 55 parts of powdered clayand 5 parts of 40% commercial formalde- ,hyde solution to be entirelysatisfactory. This.

the surface of the paper plate to repel the ink 36 on the inking roll,in conjunction with the wellknown chemicals, which are used inlithographic repellents, such as phosphoric acid for example.

The plate is then dried.

The clay or silica or like material provides an E5 even texture or grainon the surface of the paper plate, which is necessary for the bestresults in receiving and retaining the applied marking material. Thesurface of the thus coated paper plate contains a multitude of tiny mdepressions which receive the marking material used in preparing theplate and help this marking material to adhere tenaciously to the plate.The size and character of such depressions may be controlled byrendering that surface 1% alkaline to redissolve or soften the binder,as by treatment with ammonia, and/or regulating the temperature and rateof drying. Formaldehyde or any suitable acid may then be applied to thecoating to render it insoluble in the water or W repellents used inlithography.

I have found that a paper, so waterproofed as not to expanddeleteriously when. wet in the lithographing process in which it isused, and

which provides a surface of substantially equal affinity for lithographywater and grease makes a satisfactory plate having the qualities andproperties necessary for successful practical use.

, I have said thatthe surface of the coated pa- 4c per plate of myinvention has a substantially equal aiiinity for lithography grease andwater. By that I mean that it has the following properties with respectto such grease and water. The

initial greasy marking material, applied to the 45 plate, forms auniform and continuous coating over the areas marked, which coatingadheres to the plate with such tenacity that it will not be displaced-by the lithography water which is applied over the entire surface ofthe plate. 50

coated with a coating such as above described w the plate for thelithography water and grease secures the important result that neithersuch water nor grease materially displaces the other. If it did, ablurred impression would result after an undesirably few impressions hasbeen taken. The afllnities of the surface of the plate to thelithography water and grease need not be exact ly equal, but are sonearly equal that the impressions will not become blurred in the normaluse of the plate in commercial lithography.

In order to make the plate photo-sensitive I may add to the coating anyof the well-known photo-sensitive chemicals so that the plate will takephoto impressions which may be developed on exposure to light in themanner wellknown to the art.

I prefer to coat the paper on both sides. In such case I have found itadvantageous to attach to each side of the coated plate, preferably byembossing, a sheet of thin paper, such as tissue paper, which protectsthe coated surface when the plates are'assembled in a pile as'they wouldconveniently be for practical use. The attached paper is alsoadvantageous in-provid- 'ing a means for holding in place a sheet fromwhich marks are to be reproduced on the surface of the plate, such as asheet of carbon paper.

I claim: a

1. A plate for .use in lithography comprising a water-repellent paperbase coated with a coating comprising casein, silicious clay andformaldehyde, said coating possessing an amnity for li- I ing sheetwhich is substantially non-stretching when subjected to thelithographing process, and a flexible coating comprising a filler,casein and formaldehyde firmly adhering to said sheet, the surface ofsaid coating having lithographic prop erties.

- JOE V. R. SHEPHERD.

